Add noexcept to filesystem::path query functions

In the standard these member functions are specified in terms of the
potentially-throwing path decompositions functions, but we implement
them without constructing any new paths or doing anything else that can
throw.

	PR libstdc++/71044
	* include/bits/fs_path.h (path::has_root_name)
	(path::has_root_directory, path::has_root_path)
	(path::has_relative_path, path::has_parent_path)
	(path::has_filename, path::has_stem, path::has_extension)
	(path::is_absolute, path::is_relative, path::_M_find_extension): Add
	noexcept.
	* src/c++17/fs_path.cc (path::has_root_name)
	(path::has_root_directory, path::has_root_path)
	(path::has_relative_path, path::has_parent_path)
	(path::has_filename, path::_M_find_extension): Add noexcept.

From-SVN: r268713

libstdc++-v3/ChangeLog

+2019-02-09  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/71044
+	* include/bits/fs_path.h (path::has_root_name)
+	(path::has_root_directory, path::has_root_path)
+	(path::has_relative_path, path::has_parent_path)
+	(path::has_filename, path::has_stem, path::has_extension)
+	(path::is_absolute, path::is_relative, path::_M_find_extension): Add
+	noexcept.
+	* src/c++17/fs_path.cc (path::has_root_name)
+	(path::has_root_directory, path::has_root_path)
+	(path::has_relative_path, path::has_parent_path)
+	(path::has_filename, path::_M_find_extension): Add noexcept.
+
 2019-02-06  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/89102 (partial)

libstdc++-v3/include/bits/fs_path.h

@@ -359,16 +359,16 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     // query
 
     [[nodiscard]] bool empty() const noexcept { return _M_pathname.empty(); }
-    bool has_root_name() const;
-    bool has_root_directory() const;
-    bool has_root_path() const;
-    bool has_relative_path() const;
-    bool has_parent_path() const;
-    bool has_filename() const;
-    bool has_stem() const;
-    bool has_extension() const;
-    bool is_absolute() const;
-    bool is_relative() const { return !is_absolute(); }
+    bool has_root_name() const noexcept;
+    bool has_root_directory() const noexcept;
+    bool has_root_path() const noexcept;
+    bool has_relative_path() const noexcept;
+    bool has_parent_path() const noexcept;
+    bool has_filename() const noexcept;
+    bool has_stem() const noexcept;
+    bool has_extension() const noexcept;
+    bool is_absolute() const noexcept;
+    bool is_relative() const noexcept { return !is_absolute(); }
 
     // generation
     path lexically_normal() const;
@@ -433,7 +433,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
     void _M_append(basic_string_view<value_type>);
     void _M_concat(basic_string_view<value_type>);
 
-    pair<const string_type*, size_t> _M_find_extension() const;
+    pair<const string_type*, size_t> _M_find_extension() const noexcept;
 
     template<typename _CharT>
       struct _Cvt;
@@ -1102,21 +1102,21 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   }
 
   inline bool
-  path::has_stem() const
+  path::has_stem() const noexcept
   {
     auto ext = _M_find_extension();
     return ext.first && ext.second != 0;
   }
 
   inline bool
-  path::has_extension() const
+  path::has_extension() const noexcept
   {
     auto ext = _M_find_extension();
     return ext.first && ext.second != string_type::npos;
   }
 
   inline bool
-  path::is_absolute() const
+  path::is_absolute() const noexcept
   {
 #ifdef _GLIBCXX_FILESYSTEM_IS_WINDOWS
     return has_root_name() && has_root_directory();

libstdc++-v3/src/c++17/fs_path.cc

@@ -1530,7 +1530,7 @@ path::parent_path() const
 }
 
 bool
-path::has_root_name() const
+path::has_root_name() const noexcept
 {
   if (_M_type() == _Type::_Root_name)
     return true;
@@ -1540,7 +1540,7 @@ path::has_root_name() const
 }
 
 bool
-path::has_root_directory() const
+path::has_root_directory() const noexcept
 {
   if (_M_type() == _Type::_Root_dir)
     return true;
@@ -1556,7 +1556,7 @@ path::has_root_directory() const
 }
 
 bool
-path::has_root_path() const
+path::has_root_path() const noexcept
 {
   if (_M_type() == _Type::_Root_name || _M_type() == _Type::_Root_dir)
     return true;
@@ -1570,7 +1570,7 @@ path::has_root_path() const
 }
 
 bool
-path::has_relative_path() const
+path::has_relative_path() const noexcept
 {
   if (_M_type() == _Type::_Filename && !_M_pathname.empty())
     return true;
@@ -1589,7 +1589,7 @@ path::has_relative_path() const
 
 
 bool
-path::has_parent_path() const
+path::has_parent_path() const noexcept
 {
   if (!has_relative_path())
     return !empty();
@@ -1597,7 +1597,7 @@ path::has_parent_path() const
 }
 
 bool
-path::has_filename() const
+path::has_filename() const noexcept
 {
   if (empty())
     return false;
@@ -1783,7 +1783,7 @@ path::lexically_proximate(const path& base) const
 }
 
 std::pair<const path::string_type*, std::size_t>
-path::_M_find_extension() const
+path::_M_find_extension() const noexcept
 {
   const string_type* s = nullptr;